Fire Department officials said workers were continuing efforts to extricate the bodies from the twisted wreckage.

The force of the crash pushed the locomotive engine pulling the commuter train backward into a passenger car, and both toppled over, igniting in flames. At least seven cars from the freight train derailed, although most remained standing across the tracks.

Both trains were traveling at about 40 miles per hour, according to Metrolink spokesman Denise Tyrrell.

Distraught relatives and friends of passengers awaited word on their loved ones as rescue workers delicately dismantled a crushed Metrolink passenger car in search of victims.

The search was expected to last into Sunday as firefighters dug deeper into the wreckage.

Firefighters put out a fire under part of the train and pulled people from the passenger car, which was rested on its side with the Metrolink engine shoved inside it. Two other Metrolink cars remained upright.

Rescue agencies work to free trapped victims at the scene of the crash

Rescue agencies work to free trapped victims at the scene of the crash

An injured man is rushed to hospital - many more awaited rescue at the scene

The train wreck shocked those who first saw it.

Leslie Burnstein heard screams of agony as she ran through a smoky haze toward a wrecked train where dozens of bloodied passengers were still trapped inside. She pulled victims out one by one, some weeping as they looked about at the destruction.

'It was horrendous,' said Burnstein, a psychologist who saw the train crash from her home. 'Blood was everywhere. ... I heard people yelling, screaming in pain, begging for help.'

Passenger Willie Castro, 67, who was in the commuter train’s last carriage, said: ‘All of a sudden we heard a big crash. Everyone flew all over the place. It was just a big crash. A boom.’

The engine of the Union Pacific freighter was left on its side, its nose against the Metrolink wreckage. The rest of the freight train was accordioned behind it. Fire Chief Douglas Barry said heavy equipment was brought in to take apart cars, including one that some victims still trapped inside.

Firefighters work overnight to search for survivors in the wreckage of the Metrolink commuter train

Firefighters work overnight to search for survivors in the wreckage of the Metrolink commuter train

Rescuers crawl over the Metrolink train in a hunt for survivors

Rescuers crawl over the Metrolink train in a hunt for survivors

'This is the worst accident I've ever seen,' Mayor Antonio Villaraigosa said. 'Clearly the injuries are going to mount and so are the fatalities.'

Marc Eckstein, medical director for the city Fire Department, said 135 people were transported to hospitals - about 85 of them in serious or critical condition.

In the initial hours after the disaster, firefighters treated the injured at three triage areas near the wreck, and helicopters flew in and out of a nearby landing area on medical evacuation flights.

Rescuers worked atop the wreckage and through breaches in the passenger car to reach victims. Dazed and injured passengers sat on the ground.

One injured man told KNBC-TV he boarded the Metrolink train in suburban Burbank and was talking with a fellow passenger when the crash occurred.

'Within an instant I was in my friend's lap. It was so quick. It was devastating,' he said.

Antonio Villaraigosa, the city’s mayor, said: ‘I am heartbroken to see this number of injuries, devastation, carnage.’

Devastating: a passenger is helped from one of the mangled carriages

Devastating: a passenger is helped from one of the mangled carriages

Metrolink spokeswoman Denise Tyrrell said the Metrolink train left Union Station in downtown Los Angeles and was headed northwest to Moorpark in Ventura County. The trains collided about 4:30 p.m. in the Chatsworth area of the San Fernando Valley.

'I do not know what caused the wreck,' said Tyrrell who broke down crying. 'Obviously two trains are not supposed to be on the same track at the same time.'

Union Pacific spokeswoman Zoe Richmond said it was common in California for freight and commuter trains to share the same track.

Firefighters pull a seriously injured woman from the wreckage

Firefighters pull a seriously injured woman from the wreckage

The crash happened in an area where the tracks form a 'U' shape, about 2,500 feet (760 metres) wide. At the top of the bend is a 500-foot (150-metre) long tunnel that runs beneath Stoney Point Park, popular with climbers for its large boulders.

On the north side of the tunnel, there is a siding, a length of track where one train can wait for another to pass, Tyrrell said.

The federal investigation into the crash will be headed by the National Transportation Safety Board, said Steven Kulm, a spokesman for the Federal Railroad Administration. The FRA will conduct a review of whether any federal rail safety regulations were violated.

Asked how the two trains ended up on the same track, Kulm said, 'We are nowhere near having any information on that.'

First aid is administered to passengers in a triage area

First aid is administered to passengers in a triage area

Prior to Friday, the worst disaster in Metrolink's history occurred on January 26, 2005, in suburban Glendale when a man parked a gasoline-soaked SUV on railroad tracks. A Metrolink train struck the SUV and derailed, striking another Metrolink train traveling the other way, killing 11 people and injuring about 180 others.

Juan Alvarez was convicted this year of murder for causing that crash.

LA County firefighters carry an injured person into a waiting helicopter

LA County firefighters carry an injured person into a waiting helicopter